Electron space discharge device



March 29, 1955 G. w. BAKER 2,705,311

ELECTRON SPACE DISCHARGE DEVICE Filed Aug. 30, 1951 2 Sheets-Sheet 2 NV 0 Geaea 4256 United States Patent ELECTRON SPACE DISCHARGE DEVICE George W. Baker, Stamford, Conn.

Application August 30, 1951, Serial No. 244,309

2 Claims. (Cl. 339-145) This invention relates to electron space discharge devices in which an electrode assembly comprising at least an anode and a cathode is enclosed in a hermetically sealed envelope.

Some of the features of invention disclosed in the present application but not claimed therein constitute the subject-matter of co-pending application Serial No. 244,310, filed August 30, 1951.

Among the objects of the invention is an electron space discharge device of the foregoing type capable of Withstanding severe and continuous, as well as abrupt, vibrations and mechanical shock without any impairment of the desired electrical characteristics of such device, and a method for producing the same.

Another object of the invention is a rugged electron space discharge device embodying novel features which make it possible to simplify the critical problems connected with their manufacture and a method for making it possible to manufacture such tubes on a mass production basis with a high degree of uniformity of their operating characteristics.

The foregoing and other objects of the invention will be best understood from the following description of exemplifications thereof, reference being had to the accompanying drawings, wherein:

Fig. 1 is a vertical cross-sectional view of one form of a multi-electrode electron space discharge tube exemplifying the invention;

Fig. 2 is a vertical cross-sectional view of the same tube in a direction transverse to Fig. 1;

Fig. 3 is a cross-sectional view along line 3-3 of Pi l;

g ig. 4 is a cross-sectional view along line 44 of Fig. 1;

Fig. 5 is a cross-sectional view along line 55 of Fig. 1;

Fig. 6 is a cross-sectional view along line 6-6 of although the principles of the invention are applicable to all types of electron tubes, their application will be explained herein in connection with a pentode-type tube which has a very wide use as a voltage gain and power 'amplifier, and is shown in Figs. 1 to 6.

The tube shown comprises an evacuated, generally elongated tubular envelope 10 of vitreous material, such as glass, which encloses an electrode assembly generally designated 11. The electrode assembly 11 comprises a plurality of electrodes which are connected to a plurality of leads 12, 13, 14, 15, 16, 17 and 18 hermetically sealed through an electrically insulated terminal end wall portion 19 of the envelope 10 to provide external circuit connections to the electrodes. The terminal end wall portion 19 is made in the form of a wafer-like stem of vitreous material sealed around portions of the lead conductors 12 to 18 which are shown arrayed thereon in a generally circular row. The wafer-like lead stem 19 extends in a direction transverse to the envelope 10 and is fused to its lower end border.

Referring to Figs. 1 and 2, the electrode assembly 11 comprises an indirectly heated cathode 21, a control grid 22, a screen grid 23 and an anode 24, all extending longitudinally generally parallel to a common axis of the electrode assembly 11. An additional auxiliary electrode structure 25 is interposed across the electron path between the anode 24 and the screen grid 23.

Heretofore, the method used to procure a ruggedized tube capable of withstanding severe and continuous, as

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well as abrupt, vibrations and mechanical shock was by providing the tube with an extremely rigid electrode assembly. This was generally found to be sufiicient to withstand most normal shock and vibration. However, extreme impact stresses would tend to break the vitreous envelope and/or portions of the electrode assembly.

According to one phase of the invention, the tube is provided with a relatively flexibly coupled substantially rigid base 60 which will permit limited movement between the base 60 and the envelope 10 of the tube and thereby result in a tube capable of absorbing an enormous amount of impact stress Without fracturing.

One phase of the invention concerns itself with providing an electron space discharge device comprising a hermetically sealed envelope 10 enclosing an electrode assembly, which envelope 10 is attached to a substantially rigid base 60 by a relatively pliable material 65 which is arranged so that when the device is subjected to severe and continuous, as well as abrupt, vibrations and mechanical shock, such relatively pliable material will absorb a substantial amount of such shock, thereby preventing any impairment of the desired electrical characteristics of such device.

Referring to Figs. 1 and 2, in the specific form shown, the base 60 comprises a thin generally circular cup-like structure which encloses a substantial part of the lower portion of the envelope 10. The base 60 is generally composed of an electrically insulating material, such as a phenolic condensation product. The bottom portion or end 61 of the base has aflixed therein a plurality of rigid metal connector pins 62 extending therefrom in a plane parallel to the common axis of the tube and arrayed thereon in a generally circular row. A plurality of flexible leads 63 which will permit movement of the envelope 10 relatively to the base 60 are loosely connected between the rigid connector pins 62 and each stem lead 12 to 18, respectively, held fixed in the end wall portion 19 of the tube. The rigid connector pins 62 serve to provide external circuit connections through the flexible leads 62 and the stem leads 12 to 18 to the various electrodes of the electrode assembly 11. The base terminal pins 62 shown are of the conventional hollow metal type through which a length of the respective flexible connector leads 63 are threaded in a conventional way for joining the ends of the flexible leads protruding through the outer tip of the respective terminal pins 62 by soldering followed by cutting of the projecting excess portion of the flexible leads. The soldering of the flexible leads 63 to the outer ends of the terminal pins 62 is done in a conventional way after joining the base 60 to the envelope.

The space separating the inner surface of the rim of the base 60 and the corresponding facing outer surface of the envelope 10 contains elastomer material 65 which forms a bond with both the base 60 and with the envelope 10. The cement forms a sutficiently stiff bond that permits limited vibration suppressing movement between the envelope and the base when subjected to disturbing vibrations-but which resist any substantial movement therebetween. Accordingly, a substantial amount of any impact or vibration stress directed against the tube will be absorbed by the pliable junction layer 65 thus permitting the tube to withstand large impacts and vibrations without fracture. On the other hand, the bond or junction layer between the base and the envelope is made sufficiently stilt so that the tube with its base may be readily removed as a whole from the base socket by gripping the envelope and pulling it out of the socket.

It is of advantage to combine a foaming agent with the bonding material used for forming the pliable joint between the base and the envelope so that when curing the bonding material gas is developed in the bonding layer causing the bonding layer to expand and thus greatly increase the bond between the junction layer with the base and envelope, respectively, while at the same time increasing the pliability of the junction layer and also forming a moisture resistant seal which prevents entry of moisture and corrosion of the metal elements within the base.

Any of the known rubber, rubber-like or elastomer materials which may be expanded into foam rubber body in the curing process or otherwise may be used as the bonding material for providing the pliable junction layer between the envelope and the base in accordance with the invention.

In this treatment the layer of bonding material is expanded by its foaming agent, thereby increasing its union with the coated surfaces of the base and envelope respectively and also increasing or giving the junction layer interposed therebetween the desired pliability.

Very good results are obtained by using as a bonding material standard commercially available grades of silicon rubber paste which, in curing, solidifies into an expanded stable rubberlike body, such as the commercially avail able silicon rubber paste known as Dow-Corning Silastic No. 110. The following procedure is used for forming with such silicon rubber paste a pliable junction between the base 60 and the tube envelope 10. A thin stratum or film of the silicon rubber paste is applied to the facing surfaces of the base 60 and the envelope which are to be joined. The thin surface coating is thereafter partially cured by heating for about minutes at a temperature of about 165 C. while exposed to air, resulting in surface coating films which are free from foam or gas spaces and which adheres firmly to the coated surfaces.

In general, a thin coating of the bonding material is first applied to the facing surfaces of the base and the envelope which are to be joined to each other. The coating layer or stratum so applied is partially cured, for instance, by heating in air so that it adheres tightly to the underlying surfaces of the base and the envelope, respectively.

After the partial curing the base and envelope coatings, the loose flexible leads 63 are connected, as by soldering, to the stem leads 12 to 18 of the envelope.

The envelope is then positioned within the base 60 and held therein in properly spaced position as by a suitable jig. The gap space between the film coated base and the film coated envelope portions is then filled with the required quantity of the bonding material including the foaming agent out of which the pliable joint is to be formed. Thereafter, the base with the envelope so joined to each other are subjected to a treatment in which the bonding material placed therebetween is cured at an elevated temperature, for instance, thereby causing the bonding layer to be firmly united with the coated surfaces of the base 60 and the envelope 10 respectively.

After completing the partial curing, the loose flexible leads 63 are connected to the connector pins 62 of the base 60 in a conventional way by joining thereto portions of the leads 63 passing therethrough, as by soldering.

With the so-coated envelope portion held in its position within the so-coated base 60, the gap spacing therebetween is filled with the silicon rubber paste to form the junction layer 65.

The so completed assembly of envelope 10 and base 60-With its layer 65 of silicon rubber paste filling the gap between the film coated surfaces of the base and envelope respectively-is then subjected to a curing treatment at 140 C. for about two to four hours, within a suitable furnace, for instance. In this curing treatment, the silicon rubber paste generates gases which cause expansion of the bonding layer 65 formed thereof, thereby providing a tight union and anchoring junction between the expanded junction layer 65 and the coated surfaces of the base and envelope, respectively. In addition, the cured silicon rubber layer 65 forms a foam-like rubber structure which constitutes a seal against entry of moisture or fungi foreign matter into its interior and into the interior of the base sealed thereby.

A tube envelope so joined to the base will permit limited vibration suppressiing movement of the envelope within the base while providing a firm connection therebetween which permits withdrawal of the tube from the socket by the application of pulling forces to the upper portion of the envelope projecting above the base. Such tube will also meet the standard accepted torque test in which the base is held fixed against rotation and a torque of 20 inch-pounds is applied to the envelope without disturbing or breaking the union between the base and the envelope.

The curing of the pliable material with its foaming agent mixture provides an effective moisture-resistant bond with the two films. The mixture expands during curing to press tightly against the facing surfaces of the envelope and the base and provides a sealed secure bond between the base 60 and the envelope 10. This tight bond permits the envelope 10, under stress, limited twisting or bending within the base 60 wherebythe pliable material 65 absorbs a substantial part of the stresses exerted against the tube and prevents fracturing of the envelope 10 and/ or the electrode assembly 11.

The end or bottom portion 61 of the base is kept free of the pliable material 65 in order to prevent electrical leakage between the various metal elements. The excess cured pliable material 65 that has expanded beyond the boundary edges of the base 60 is trimmed off.

It will be apparent to those skilled in the art that the novel principles of the invention disclosed herein in connection with specific exemplifications thereof will suggest various other modifications and applications of the same. It is accordingly desired that in construing the breadth of the appended claims they shall not be limited to the specific exemplification of the invention described herein.

I claim:

1. In an electron space charge device: an assembly of electrodes, an envelope enclosing said assembly, each of said electrodes having at least one electrode lead sealed through a terminal wall portion of said envelope to provide outer lead portions extending beyond said envelope, a substantially rigid base including a plurality of outwardly extending metallic connector pins, said base having a hollow outer base section enclosing said sealedthrough outer lead portions and having inner surface junction portions spacially separated from facing outer surface junction portions of said envelope, a relatively thick junction body of pliable, gas expanded elastomer material positioned between and having spaced junction surfaces joined by a tight secure bond to said facing outer and inner surface junction portions of said base and said envelope to provide a shock-absorbing movement of said envelope relatively to said base, and a plurality of flexible connector leads of materially greater length than the spacing between the outer ends of said outer electrode lead portions and said connector pins extending through said hollow base section and electrically connected between said connector pins and said outer electrode lead portions to provide external connections to said electrodes.

2. A device as claimed in claim 1, said pliable elastomer material comprising a silicone elastomeric resin to provide moisture-resistant bond between the envelope and the ase.

References Cited in the file of this patent UNITED STATES PATENTS 2,000,395 Jones May 7, 1935 2,079,798 Geyer May 11, 1937 2,292,002 Yamashita Aug. 4, 1942 2,354,642 Anderson Aug. 1, 1944 2,398,595 Powell Apr. 16, 1946 2,578,415 Franklin Dec. 11, 1951 2,627,536 Elliott Feb. 3, 1953 

